EXPLICITLY CORRELATED GAUSSIAN FUNCTIONS IN VARIATIONAL CALCULATIONS - THE GROUND-STATE OF THE BERYLLIUM ATOM

Explicitly correlated Gaussian functions are applied to extensive vari ational calculations of the S-1 ground state of the beryllium atom. Th e convergence of the energy with respect to the basis-set expansion le ngth is investigated. The nonrelativistic clamped-nuclei energy comput ed from a 1200-term wave function equals -14.667 355 hartree and is in error by about 1 cm(-1). This is the lowest variational upper bound t o the beryllium ground-state energy reported to date and it shows that recent empirical estimates of the nonrelativistic energy of the Be at om lie slightly too high. Several expectation values, including powers of interparticle distances and the Dirac delta function, are computed . The nuclear magnetic shielding constant, the magnetic susceptibility , the specific mass shifts, the transition isotope shift, and the elec tron density at the nucleus position are evaluated.